This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 11(1999)-149796 filed on May 28, 1999, the entire content of which is incorporated herein by reference.
The present invention is generally directed to a vehicle braking system. More particularly, the present invention pertains to a braking force distribution control device in which a predetermined relationship is established between the braking force of the rear wheel and the braking force of the front wheel.
Japanese Unexamined Patent Publication No. Hei. 9-11878, published in 1997, discloses a braking force distribution control device that is designed to execute a braking force distribution control in the vehicle longitudinal direction. The braking force distribution control is made on the basis of the difference between the speed of a front wheel and the speed of a rear wheel, and is initiated when the vehicle body deceleration is in excess of a set value or a vehicle body reference deceleration. More specifically, the braking force distribution control is initiated upon the occurrence of one of the following.
1) When the vehicle body deceleration exceeds a first set value and the wheel speed differential between the front wheel and the rear wheel deviates from a set value.
2) Despite a wheel speed differential, when the vehicle body deceleration exceeds a second set value which is greater than the first set value.
In this known braking force distribution control device, the braking force distribution control is initiated when the vehicle deceleration exceeds the set value. This makes it possible to initiate the control rapidly when a rapid operation of a brake pedal or a rapid braking operation is performed in which the change of the wheel speed differential is slow due to gradual load shift of the vehicle body, as compared with a similar device which is designed to initiate the control based on only the wheel speed differential between the rear and front wheels.
However, because the rapid braking operation causes the vehicle body deceleration to increase after the increase of the wheel deceleration, the initiation of the braking force distribution control in this known device is delayed.
In addition, in general, a dual brake circuit system such as an X-piping system or a longitudinal piping system is employed in automotive vehicles. If one of hydraulic pressure lines fails, it is possible that the vehicle body deceleration exceeds the set value, which may unexpectedly initiate the braking force distribution control, thereby lowering the braking force applied to the vehicle.
In light of the aforementioned drawbacks, a need exists for a braking force distribution control device for automotive vehicles which is capable of initiating a braking force distribution control as quickly as possible upon rapid braking operation.
A need also exists for a braking force distribution control device for automotive vehicles which prevents initiation of the braking force distribution control when one of hydraulic pressure lines fails.
According to one aspect of the present invention, a braking force distribution control device for an automotive vehicle having a plurality of wheels includes wheel speed detecting means for detecting a wheel speed of each of the plurality of wheels, wheel deceleration calculating means for calculating a wheel deceleration of each of the plurality of wheels based on the detecting results of the wheel speed detecting means, and braking control means for controlling a braking force of a rear wheel to execute a braking force distribution control in such a manner that the braking force of the rear wheel is adjusted to have a predetermined relationship to the braking force of a front wheel depending on a comparison between the wheel speed of the front wheel and the wheel speed of the rear wheel based on the detecting results of the wheel speed detecting means, the braking control means initiating the braking force distribution control when at least one of the wheel decelerations of the plurality of wheels exceeds a set value.
The braking force distribution control is initiated when at least one of the decelerations of the wheels exceeds a set value, which makes it possible to initiate the braking force distribution control more rapidly upon the occurrence of a rapid braking operation when compared.
The braking force distribution control device can also include a first wheel cylinder applying a braking force to a first wheel of the plurality of the wheels and connected to a first hydraulic pressure line and a second wheel cylinder applying a braking force to a second wheel of the plurality of the wheels and connected to a second hydraulic pressure line which is disconnected from the first hydraulic pressure line. The braking control means initiates the braking force distribution control when both of the decelerations of the first and second wheels exceed the set value. Thus, when one of the first and second hydraulic pressure lines fails, the deceleration of either the first wheel or the second wheel does not exceed the set value. This makes it possible to prevent an unexpected initiation of the braking force distribution control to thereby avoid the lowering of the braking force applied to the vehicle.
The braking control means can also be designed to initiate the braking force distribution control when the deceleration of a driving wheel exceeds the set value. In the event both the acceleration and brake pedals are depressed concurrently the deceleration of the driving wheel does not exceed the set value, thus preventing an unexpected initiation of the braking force distribution control and avoiding the lowering of the braking force applied to the vehicle.
The braking control means can also be designed to initiate the braking force distribution control when the decelerations of all of the wheels exceed the set value. The braking force distribution device can further include a hydraulic pressure generator for generating a hydraulic pressure, wheel cylinders mounted on the front and rear wheels for applying braking forces to the respective wheels, a hydraulic pressure line connecting the hydraulic pressure generator and each of the front and rear wheel cylinders, and a hydraulic pressure control valve disposed in the hydraulic pressure line for regulating the hydraulic pressure applied to the corresponding wheel cylinder. The braking control means then controls the hydraulic pressure control valve of the rear wheel for adjusting the hydraulic pressure of the wheel cylinder of the rear wheel to establish a predetermined relationship between the wheel cylinder pressure of the front wheel and the wheel cylinder pressure of the rear wheel.
According to another aspect of the invention, a braking force distribution control device for an automotive vehicle having a plurality of wheels that includes a pair of front wheels and a pair of rear wheels, comprising:
a pressure generator for generating hydraulic pressure;
a plurality of wheel cylinders each mounted on one of the wheels and connected to the pressure generator for applying a braking force to each of the plurality of wheels;
a plurality of wheel speed sensors each operatively associated with one of the wheels for detecting a wheel speed of each wheel;
means for calculating a wheel deceleration of each of the plurality of wheels based on the wheel speeds detected by the wheel speed sensors; and
a controller which initiates braking force distribution control when at least one of the wheel decelerations of the plurality of wheels exceeds a set value so that the braking force applied to one rear wheel is adjusted to have a predetermined relationship to a braking force applied to one front wheel depending upon a comparison of the wheel speed of the one front wheel and the wheel speed of the one rear wheel as detected by the wheel speed sensors.